Felted hydrophilic ester polyurethane foams

ABSTRACT

An ester polyurethane foam is prepared by reacting a mixture of one or more polyester polyols with one or more isocyanates and one or more silicone surfactants in the presence of a blowing agent, such as water, and other additives, such as catalysts. The cured foam is chemically treated in a caustic solution and is then felted (compressed under heat and pressure) to form a hydrophilic ester polyurethane foam having a water absorption rate of at least 30 pounds of water per square foot per minute (1.44 kPa/min). The foam also has greater water holding capacity and wet strength than cellulose.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part of U.S. patent applicationSer. No. 10/074,606, filed Feb. 12, 2002 now U.S. Pat. No. 6,756,416.This application further claims priority from U.S. ProvisionalApplication Ser. No. 60/435,277, filed Dec. 23, 2002.

This invention relates to certain ester polyurethane foams that havebeen chemically modified and then felted (compressed under heat andpressure), following which the foams have unexpectedly improved liquidabsorption and wicking. The foams may be incorporated into articles usedto wipe and absorb liquids, such as household cleaning sponges and mopheads.

BACKGROUND OF THE INVENTION

Polyurethane foams are generally prepared by the reaction of an activehydrogen-containing compound (i.e., a polyol) and a polyisocyanate, inthe presence of a blowing agent such as water, and usually a reactioncatalyst and foam stabilizer. The cellular polymer structure ofpolyurethane foam has a skeletal framework of relatively heavy strandsforming an outline for the cell structure. The skeletal frameworkstrands are connected by very thin membranes, often called windows,which form the cell walls. In open-celled foams, some of the windows areopen or torn in each cell, thus forming an interconnecting network opento fluid flow (liquid or gas). However, conventional polyurethane foamsare not sufficiently porous or open-celled to allow significant fluidflow therethrough.

Reticulation relates to methods for removing or breaking the cellwindows of polyurethane foams. Mechanical, chemical and thermal methodsfor reticulating foams are known. As one example, foam may bereticulated by melting the windows with a high temperature flame frontor explosion, which still leaves the strand network intact.Alternatively, the cell windows may be etched away using the hydrolyzingaction of water in the presence of an alkali metal hydroxide. See U.S.Pat. Nos. 3,125,542; 3,405,217; 3,423,338; 3,425,890 and 4,670,477 fordescriptions of various reticulating methods for polyurethane foams.

Household cleaning sponges and mop heads most commonly are formed fromcellulose. Paper pulp is the primary ingredient for cellulose sponges.The pulp is reacted with carbon disulfide to form a soluble cellulosexanthate compound. This compound is dissolved into a honey-like liquidviscose and mixed with reinforcing fibers to add strength to the pulpmixture. The cellulose is formed with a double cell structure toreplicate natural sea sponges. Sodium sulfate crystals are added to thepulp, and this mixture is heated in a mold to melt the crystals. Heatingregenerates the mix to pure cellulose and leaves the signature spongeholes where the crystals have melted away. Bleaching chemicals andhumectants maintain the moisture level and color purity of the cellulosesponge. While the cellulose has good water absorption and wicking, ithas lower wet integrity than other materials. Moreover, upon drying, thecellulose becomes hard and brittle such that it must be pre-wet beforeusing for wiping.

Open celled ester and ether polyurethane foams have greater softness andflexibility than cellulose, and retain flexibility upon drying withouthumectants. As compared to cellulose, foams have greater wet strength,better wet integrity and exhibit less swelling when wet. Foams also canbe foamed to have a double cell structure to more resemble natural seasponges. Generally, polyurethane foams can be produced more cheaply thancellulose. However, polyurethane foams are hydrophobic, lacking goodliquid absorption and wicking characteristics, which makes them lesssuitable for household sponges and mop heads. Even after thepolyurethane foams are post-treated with surfactants in an attempt toimprove water absorption and wicking, they still do not match theperformance of cellulose for these properties.

Reticulated polyurethane foams have been used as components of filters.Such foams also have been suggested for use as components of householdsponges, particularly for the abrasive surface presented by areticulated foam. See U.S. Pat. Nos. 3,857,133 and 5,640,737. The artstill seeks polyurethane foams suitable to replace cellulose materialsas liquid absorbing and wicking components of household sponges and mopheads.

SUMMARY OF THE INVENTION

According to the invention, a hydrophilic ester polyurethane foam ismade by first forming a cellular polyurethane foam that has a network ofat least some strands and at least some cell windows by mixing togethercertain foam-forming components. Typically, the recipes for polyurethanefoams are expressed in terms of parts by weight per 100 parts polyol.Thus, for each 100 parts by weight of a polyester polyol, the foamformulation according to the invention includes: from 20.0 to 62.0 partsby weight of an isocyanate; from 1.5 to 5.0 parts of a blowing agent,such as water; from 0.5 to 2.0 parts of a blow catalyst; from 0 to 0.3parts of a gel catalyst, and from 1.0 to 3.0 parts of a stabilizingsurfactant, such as a silicone surfactant. Other additives such asantimicrobial additives, double cell additives, dyes, pigments,colorants, crosslinking additives, fragrances, detergents and extendersmay also be incorporated into the foam formulation.

After the foam forming components have been mixed together, the foam ispermitted to rise and cure, preferably under atmospheric temperature andpressure. The resulting foam has pore sizes preferably in the range offrom 70 to 130 pores per linear inch (27.6 to 51.2 pores per cm), mostpreferably 70 to 90 pores per linear inch (27.6 to 35.4 pores per cm),but may also have a double cell or sea sponge-like structure. Thepreferred double cell structure has a distribution of larger and mediumsized cells scattered across a background of finer cells. The largercells may range from 0.06 to 0.09 inches (1.52 to 2.29 mm) in diameter.

The cured foam is cut into slabs and then chemically treated byimmersing the slab in a heated caustic bath for from three to fifteenminutes, preferably from six to ten minutes. One preferred caustic bathis a sodium hydroxide solution (from 5.0 to 10.0 percent, preferably7.5% NaOH) that is heated to from 70° F. to 160° F. (21 to 71° C.),preferably from 120° F. to 160° F. (49 to 71° C.). The caustic solutionetches away at least a portion of the cell windows within the foamcellular structure, leaving behind a hydrophilic ester polyurethanefoam. The treated foam is compressed between calendaring rolls, and thenrinsed thoroughly and oven dried.

After treating, the foam is felted by compressing the foam to fromone-half (½) to one-twentieth ({fraction (1/20)}) of its initialthickness, preferably from one-third (⅓) to one-eighth (⅛) of itsinitial thickness, and heating the compressed foam at a temperature offrom 340 to 380° F. (171 to 193° C.) for from 10 to 60 minutes.

After felting, the foam structure comprises a hydrophilic esterpolyurethane foam with good wicking characteristics that will absorbwater at a rate of at least about 30 pounds of water per square foot perminute (1.44 kPa/min), preferably at least 35 pounds of water per squarefoot per minute (1.68 kPa/min). The foam also has greater water holdingcapacity and wet strength than cellulose. The felted hydrophilic esterpolyurethane foam does not swell appreciably upon absorbing andretaining liquids and would make an ideal component of a householdsponge or mop head.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hydrophilic ester foams according to the invention are preparedpreferably by mixing together the polyol component with the surfactants,catalysts, blowing agents and other additives, forming a polyol pre-mix.To the polyol pre-mix is added the isocyanate component. The foammixture is then allowed to rise and cure, preferably under atmosphericconditions, to form the hydrophilic ester polyurethane foam. Thefoam-forming process may be carried out batch-wise, semi-continuously orcontinuously.

Polyester polyurethane foams are more hydrophilic than polyetherpolyurethane foams due to the increased polarity of the carboxylic acidgroups. Suitable polyester polyols for producing flexible polyesterpolyurethane foams are well known in the industry. Illustrative of suchsuitable polyester polyols are those produced by reacting a dicarboxylicand/or monocarboxylic acid with an excess of a diol and/or polyhydroxyalcohol, for example, adipic acid, glutaric acid, succinic acid,phthalic acid or anhydride, and/or fatty acids (linolic acid, oleic acidand the like) with diethylene glycol, ethylene glycol, propylene glycol,dipropylene glycol, 1,4-butanediol, neopentyl glycol,trimethylolpropane, trimethylolethane, and/or pentaerythritol. Examplesof these polyols are LEXOREZ 1102-50 or LEXOREZ 1102-60 from InolexChemical Company or FOMREZ 50 or FOMREZ 60 from Crompton Corporation.Other suitable polyester polyols can be prepared by reacting a lactonewith an excess of a diol such as caprolactone with propylene glycol. SeeU.S. Pat. No. 4,331,555 for further discussion of suitable polyesterpolyols. Preferably, the polyester polyol is made by reacting adipicacid and ethylene glycol monomers with a glycerin initiator. Hydrophilicester polyols are typically reaction products of polyethylene glycol andadipic acid. Examples are FOMREZ 45 from Crompton and LEXOREZ 1105-HV2from Inolex Chemical Company. Most preferably, the polyol component ofthe foam-forming mixture of the invention comprises at least five (5)parts by weight, preferably ten (10) parts by weight, of a 50 hydroxylhydrophilic ester polyol. 60 hydroxyl ester polyols and mixtures of 50hydroxyl and 60 hydroxyl ester polyols and 50 hydroxyl hydrophilic esterpolyols are also preferred.

The “hydroxyl number” for a polyol is a measure of the amount ofreactive hydroxyl groups available for reaction. The value is reportedas the number of milligrams of potassium hydroxide equivalent to thehydroxyl groups found in one gram of the sample. “Functionality” of apolyol is defined as the average number of hydroxyl group sites permolecule. Preferably, the polyester polyols used to form the foams ofthe present invention have a hydroxyl number in the range of 20 to 150,more preferably in the range of 40 to 100, and most preferably in therange of 50 to 60.

The term “polyisocyanate” refers particularly to isocyanates that havepreviously been suggested for use in preparing polyurethane foams.“Polyisocyanates” include di- and poly-isocyanates and prepolymers ofpolyols and polyisocyanates having excess isocyanate groups available toreact with additional polyol. The amount of polyisocyanate employed isfrequently expressed by the term “index”, which refers to the actualamount of isocyanate required for reaction with all of the activehydrogen-containing compounds present in the reaction mixture multipliedby 100. For most foam applications, the isocyanate index is in the rangeof between about 75 to 140. In this invention, the preferred isocyanateindex is in the range of 90 to 110, most preferably 100 or below, with aparticularly preferred range of 95 to 98.

The polyester polyurethane foams are prepared using any suitable organicpolyisocyanates well known in the art including, for example,hexamethylene diisocyanate, phenylene diisocyanate, toluene diisocyanate(TDI) and 4,4′-diphenylmethane diisocyanate (MDI). The methylenediisocyanates suitable for use are diphenyl methane diisocyanate andpolymethylene polyphenyl isocyanate blends (sometimes referred to as“MDI” or “polymeric MDI”). The MDI blends can contain diphenylmethane 4,4′ diisocyanate, as well as 2, 2′ and 2, 4′ isomers and higher molecularweight oligomers and have an isocyanate functionality of from about 2.1to 2.7, preferably from about 2.1 to 2.5. Preferably, the isocyanate isselected from a commercial mixture of 2,4- and 2,6-toluene diisocyanate.A well-known commercial toluene diisocyanate is TD80, a blend of 80% 2,4 toluene diisocyanate and 20% 2, 6 toluene diisocyanate.Polyisocyanates are typically used at a level of between 20 and 90 partsby weight per 100 parts of polyol, depending upon the polyol OH contentand water content of the formulation.

One or more surfactants are also employed in the foam-formingcomposition. The surfactants lower the bulk surface tension, promotenucleation of bubbles, stabilize the rising cellular structure, emulsifyincompatible ingredients, and may have some effect on the hydrophilicityof the resulting foam. The surfactants typically used in polyurethanefoam applications are polysiloxane-polyoxyalkylene copolymers, which aregenerally used at levels between about 0.5 and 3 parts by weight per 100parts polyol. In the present invention, from 1.0 to 3.0 parts by weightper 100 parts polyol of surfactant is preferred. Surfactants, which mayfor example be organic or silicone based, such as FOMREZ M66-86A (Witco)and L532 (OSi Specialties) may be used to stabilize the cell structure,to act as emulsifiers and to assist in mixing. Most preferably, thesurfactant is a cell opening silicone surfactant in an amount from 1.5to 2.5 parts by weight per 100 parts polyol.

Catalysts are used to control the relative rates of water-polyisocyanate(gas-forming or blowing) and polyol-polyisocyanate (gelling) reactions.The catalyst may be a single component, or in most cases a mixture oftwo or more compounds. Preferred catalysts for polyurethane foamproduction are organotin salts and tertiary amines. The amine catalystsare known to have a greater effect on the water-polyisocyanate reaction,whereas the organotin catalysts are known to have a greater effect onthe polyol-polyisocyanate reaction. Total catalyst levels generally varyfrom 0 to 5.0 parts by weight per 100 parts polyol. The amount ofcatalyst used depends upon the formulation employed and the type ofcatalyst, as known to those skilled in the art. Although variouscatalysts may be used in the present invention, we have found that thefollowing ranges of catalyst amounts are satisfactory: amine catalystfrom 0.5 to 2.0 parts, per 100 parts polyol; and organotin catalyst from0 to 0.7 parts, preferably from 0 to 0.3 parts, per 100 parts polyol.

Suitable urethane catalysts useful in the present invention are allthose well known to the worker skilled in the art, including tertiaryamines such as triethylenediamine, N-methylimidazole,1,2-dimethylimidazole, N-methylmorpholine, N-ethylmorpholine,triethylamine, tributylamine, triethanolamine, dimethylethanolamine andbisdimethylaminodiethylether, and organotins such as stannous octoate,stannous acetate, stannous oleate, stannous laurate, dibutyltindilaurate, and other such tin salts.

A double-cell structure may be created to replicate the appearance ofnatural sea sponges. Materials used to create a double cell structuremay be added to the foam forming mixture. These include: castor oilderivatives, stearic acid, acetic acid and low melting point waxes.These materials create voids larger than the prevailing pores within theresulting foam structure. If used, the double-cell additive preferablyis added in an amount from 0.04 to 0.21 parts per 100 parts polyol.

A blowing agent may be included in the foam-forming composition. Themost typical blowing agent is water that may be added in amounts from1.5 to 5.0 parts per 100 parts polyol. Alternative blowing agents areliquid carbon dioxide, volatile organic compounds, such as pentane andacetone, and chlorinated compounds, such as methylene chloride, HFC's,HCFC's and CFC's.

Optionally, other additives may be incorporated into the foam-formingcomposition. The optional additives include, but are not limited to,antimicrobial compounds, stabilizers, extenders, dyes, pigments,crosslinking additives, fragrances, detergents and anti-static agents.Such additives should not have a detrimental effect on the properties ofthe final polyurethane foam. For sponge and mop head applications,preferably an antimicrobial compound is added in an amount from 0.5 to1.5 parts per 100 parts polyol.

The hydrophilic ester polyurethane foam has cell sizes preferablyranging from 70 to 130 pores per linear inch (27.6 to 51 pores per cm),most preferably 70 to 90 pores per linear inch (27.6 to 35.4 pores percm), but may also have a double cell or sea sponge-like structure. Thepreferred double cell structure has a distribution of larger and mediumsized cells scattered across a background of finer cells. The largercells may range from 0.06 to 0.09 inches (1.5 to 2.3 mm) in diameter.

The foam is then chemically reticulated to remove cell windows byimmersing the slab in a heated caustic bath for from three to fifteenminutes, preferably from six to ten minutes. One preferred caustic bathis a sodium hydroxide solution (from 5.0 to 10.0 percent, preferably7.5% NaOH) that is heated to from 70° F. to 160° F. (21 to 71° C.),preferably from 120° F. to 160° F. (49 to 71° C.). The caustic solutionetches away at least a portion of the cell windows within the foamcellular structure, leaving behind a hydrophilic ester polyurethanefoam. The treated foam is compressed between calendaring rolls, and thenrinsed thoroughly and oven dried.

After treating, the foam is felted by compressing the foam to fromOne-half (½) to one-twentieth ({fraction (1/20)}) of its initialthickness, preferably from one-third (⅓) to one-eighth (⅛) of itsinitial thickness, and heating the compressed foam at a temperature offrom 340 to 380° F. (171 to 193° C.) for from 10 to 60 minutes. Thecompression ratio is generally referred to as a firmness. For example, afoam compressed to one-third of its original thickness is a firmness 3felt. A foam compressed to one-fifth of its original thickness is afirmness 5 felt.

The invention is further illustrated, but not limited, by the followingexamples.

EXAMPLES

Cellulose sponges were obtained. The cellulose sponges of Examples C1,C2 and C3 were from 3M, Nylonge and Spontex, respectively. Based on ourtesting, cellulose had a rate of water absorption of 29 to 35 lbs.water/ft²/minute (1.39 to 1.68 kPa/min) and an effective waterabsorption of over 40% (44%).

Polyurethane foams were prepared on a laboratory scale by mixingtogether the foam-forming ingredients and pouring them into a 15″×15″(38.1×38.1 cm) cardboard box to form foam buns under atmosphericpressure (e.g., 1 atm.) and temperature (about 75° F. (24° C.)). Thefoam ingredients were mixed according to the proportions shown inTable 1. Amounts are in kilograms and are based on parts by weight perhundred parts polyol. The foams of Examples C4 to C6 are comparisonfoams not prepared according to the invention. The foams of Examples 1to 7 were prepared with formulations according to the invention, butwere not felted. The foams of Examples

Portions of the foam bun for each Example were cut into slabs andchemically treated or modified. The slabs were immersed in a heatedsolution of 7.5% sodium hydroxide in water (heated to at least 120° F.(49° C.)) for eight minutes. The slabs were then compressed betweencalendar rollers to squeeze out most of the caustic solution. The slabswere then rinsed to remove the remaining caustic solution and then driedin an oven.

Example C4 was prepared as a standard ester polyurethane foam. The foamof Example C5 was prepared with a hydrophilic polyol. Neither of thefoams from Examples C4 and C5 was chemically modified. Example C6 is athermally reticulated hydrophilic ester foam. Although the Example C6foam had completely open cells, this foam had a very low liquidabsorption rate.

TABLE 1 Polyurethane Foam Formulations C4 C5 C6 1 2 3 4 5 6 7 1102-50A100.0 0 0 100.0 90.0 75.0 90.0 90.0 90.0 90.0 F45 0 100.0 100.0 0 10.025.0 10.0 10.0 10.0 10.0 B8301 2.0 0 0 2.0 2.0 2.0 2.0 2.0 2.0 0 Y6353 00 0 0 0 0 0 0 0 2.0 SE232 0 1.0 1.0 0 0 0 0 0 0 0 DM50 0 0 0 1.5 1.5 1.51.5 0.75 0.75 1.5 Water 3.9 4.3 4.3 3.9 3.9 3.8 3.9 2.7 1.8 3.9 DCadditive 0.2 0 0 0.2 0.14 0.14 0 0.17 0.26 0.9 NEM 0.35 1.7 1.7 0.350.35 0.35 0.35 0.35 0.3 0.35 DM70 0.61 0 0 0.61 0.61 0.61 0.61 0.61 0.520.61 K5N 0.3 0 0 0.3 0.35 0.35 0.7 0.5 0.5 0.43 TD80 45.5 34.5 34.5 45.545.5 44.5 45.5 34.1 25.6 45.5 Index 98 70 70 98 98 98 98 98 98 98Density 1.70 1.88 1.88 1.91 1.61 1.61 1.86 2.85 4.05 1.78 (lbs/ft³) Poresize ppi) 70 70 70 70 70 70 100 70 70 70 Background Cell size (in.)0.035-0.085 N/A N/A 0.063-0.147 0.063-0.147 0.063-0.147 N/A 0.035-0.0850.035-0.085 0.035-0.085 Large holes

LEXOREZ 1102-50A is an ester polyol with a hydroxyl number of 50supplied by Inolex Chemical Company. F45 is FOMREZ 45, a 50 hydroxylhydrophilic ester polyol offered by Crompton. TEGOSTAB B8301 is a cellopening silicone surfactant from Goldschmidt Chemical Corporation. NIAXSilicone Y6353 is a cell opening silicone surfactant from OSiSpecialties. ULTRAFRESH DM50 is an antimicrobial additive supplied byThomson Research. The double cell additive (“DC additive”) is a castoroil derivative used to provide an optional sea sponge like structure tothe foam. KOSMOS K5N is a stannous octoate catalyst (tin catalyst) fromGoldschmidt Chemical Corporation. NEM is an amine catalyst, n-ethylmorpholine. TD80 is a toluene diisocyanate mixture comprised of 80percent 2,4-toluene diisocyanate and 20 percent 2,6-toluenediisocyanate. The “index” is the isocyanate index. The cellularstructure of the foam can be uniform or have a distribution of differentcell sizes. The uniform cell structure is described by the number ofpores per linear inch. The number is derived from a visual comparison ofthe foam to a standard. Double-cell foams have cells of varying sizes.The pores of the larger cells are within the stated range.

Sponges were cut to a desired sample size of 4.75 inches by 3.0 inchesby 0.625 inches (12.1 cm by 7.6 cm by 1.6 cm). Before testing, cellulosesponges were washed in a washing machine for two cycles to remove watersoluble materials or additives (e.g., humectants). Polyurethane foamsamples were not pre-washed.

The rate of liquid absorption (or wicking rate) was determined accordingto the following test method. The weight and dimensions of a damp spongesample are measured. The sponge has a generally rectangular front andrear surface and a certain thickness. The length and thickness of thesponge are measured to the nearest 0.01 inches (0.25 mm). The sponge iswrung out and its wrung out weight is recorded. A perforated plate isplaced in the bottom of a solid tray. Water is added to a depth of ⅛inch (3 mm) over the perforated plate. The sponge is placed on thesurface of the perforated plate and into the pool of water. One sidesurface of the sponge is held within the pool such that the front andrear faces of the sponge are held perpendicular to the surface of thewater pool. The sponge is removed after 5 seconds, and without losingwater from the sponge, the sponge is weighed. The wet weight is recordedto the nearest 0.01 grams. The rate of water absorption is reported aspounds of water per square foot per minute. It is calculated as the wetweight minus the wrung out weight divided by the length times thethickness of the sponge.

The percent effective absorption indicates the percent of water byvolume a damp sponge will retain after saturation and draining for fiveminutes. The absorption is reported in cubic inches of water held by acubic inch of sponge. The dimensions (length, width and thickness) of adamp sponge are measured to the nearest 0.01 inches (0.25 mm). The wetvolume is calculated. Wring out the sponge and record the wrung outweight to the nearest 0.01 grams. The sponge is then fully immersed in apool of warm water, squeezed to remove trapped air and allowed to absorbwater for one minute. The sponge is removed with a hook and hungvertically for five minutes to allow water to drain therefrom.Thereafter, the sponge is reweighed to the nearest 0.01grams—denominated the wet weight. The percent water retained by volumeis calculated. The percent effective absorption is the wet weight minusthe wrung out weight divided by the wet volume.

The percent total absorption indicates the total amount of water asponge can hold after draining for five minutes in a vertical positionand is expressed as a percentage of its original dry weight. The spongeis immersed in warm water and squeezed to remove trapped air. The spongeis allowed to absorb water for one minute. The sponge is then removedfrom the water with a hook and hung vertically to allow water to drainfor five minutes. Thereafter, the sponge is weighed and the drainedweight is recorded to the nearest 0.01 grams. Excess water is squeezedout of the sponge by hand. The sponge then is dried in anair-circulating oven for at least four hours at 220° F., cooled to roomtemperature and re-weighed. The dry weight of the sponge is recorded tothe nearest 0.01 grams. The percent total absorption is 100 times theamount of water retained after draining (drained weight minus dryweight) divided by the dry weight of the sponge.

Wet out time measures the time duration required for a drop of water tobe absorbed completely by a damp sponge sample. The sponge sample isimmersed in water and squeezed while in the water to remove trapped air.Upon removing from the water, the sponge is wrung out as completely aspossible. A drop of water is placed on a facing surface of the dampsponge. The time for the drop to be absorbed by the damp sponge isrecorded. The average wet out time was calculated after the test isrepeated five times.

Wipe dry is evaluated by pouring 50 grams of water on a clean levelsurface. The sample sponge is weighed before the test and after eachwiping pass across the water until no more water is absorbed. The spongeis not wrung out before or after weighing. The weight of the waterpicked up by the sponge after each pass is recorded.

Water holding capacity is measured by weighing a dry sponge, thenimmersing the sponge sample in water, squeezing to remove trapped air,soaking the sponge for five minutes, and weighing the saturated sponge.The water holding capacity is the weight of water held per gram ofsponge.

TABLE 2 Comparative Test Results - Cellulose and Prior Foams Sample C6C4 C5 Hydrophilic C1 C2 C3 Standard Hydrophilic ester 3M Nylonge Spontexester ester (reticulated) Rate of 25.1 31.7 21.4 10.8  5.2  2.7absorption % Effective  46%  43%  57%  44% N/A N/A absorption % Total1418% 1299% 1649% 1947% N/A N/A absorption Wet out Instantly InstantlyInstantly Instantly Instantly >1 min. time Wipe Test First pass 48.8 g49.4 g 44.8 g 25 g 23 g N/A Second pass 47.1 g 48.2 g 48.7 g 36 g 36 gN/A Third pass 48.6 g 43 g 44 g N/A Fourth pass 45 g 45 g N/A Waterholding 14.2 13.0 16.5 31.7 33.6 33.7 capacity (g/g foam) Density  3.52 3.91  3.77  1.70  1.88  1.88 (pcf)

TABLE 3 Comparative Test Results - Inventive Foams Sample 1 2 3 4 5 6 7unfelted unfelted unfelted unfelted unfelted unfelted unfelted Rate of28.4 24.2 25.7 22.0 27.9 20.1 20.0 absorption % Effective  23.6%  25.3% 26.4%  48.9% 41.5% 35.4%  33.8% absorption % Total 949% 1114% 1217%1867% 1037%  607% 1358% absorption Wet out Instantly Instantly InstantlyInstantly Instantly Instantly Instantly time Wipe Test First pass 46.3 g45.7 g 45.0 g 49.3 g 47.5 g 47.2 g 47.4 g Second pass 48.1 g 45.9 g 47.9g 48.0 g 48.7 g 46.7 g 46.3 g Third pass 46.2 g 46.5 g 48.5 g 48.2 gFourth pass 46.1 g 46.4 g Water holding 25.0 27.6 28.1 capacity (g/gfoam)

Referring to the data presented in Tables 2 and 3, the unfelted foams(Examples 1-7) had excellent absorption rates and performed comparableto cellulose sponges (Examples C1, C2 and C3). The Example 1 foam wasmade from a low index conventional polyester formulation and waschemically modified in a caustic solution. The Example 1 foam wickedwater and wiped similarly to the cellulose sponges, and had a greaterwater holding capacity. The foam of Example 1 performed unexpectedlybetter than foams of equivalent composition that were not chemicallymodified (Example C4) and a hydrophilic ester foam (Example C5). Thus,the combination of low index and chemical treating, particularly wherethe foam is formed with a cell opening silicone surfactant, creates anunexpectedly superior hydrophilic ester polyurethane foam. The foams ofExamples 2 to 7 performed similarly to Example 1.

Other observations are evident from the data presented. Example 2 showsthat adding 10 parts per hundred of a hydrophilic polyol can increasethe total absorption of the resulting foam. The finer cell structure ofExample 4 increased the effective and total absorption values of thefoam and improved the wipe dry. Examples 5 and 6 show the effect ofincreasing density. Example 7 shows the effect of a different surfactanttype on water absorbing properties.

Further improvements to water absorption properties were achieved oncethe foams were felted. In Tables 4 and 5, Examples 8 to 13 are accordingto the invention, and Comparative Examples C5 to C9 represent prior artcellulose or ester polyurethane foams. Comparative Examples C5, C7 andC8 were not felted. Examples 8, 9 and 10 incorporated the same esterpolyurethane formulation with at least 5 parts by weight of ahydrophilic polyester polyol made from an adipic acid and a polyethyleneglycol, but the foams of Examples 9 and 10 were felted.

TABLE 4 Sample 8 9 10 11 12 13 Fine cell Fine cell Fine cell Double cellDouble cell Double cell ester ester ester ester ester ester C7 C8polyurethane polyurethane polyurethane polyurethane polyurethanepolyurethane Cellulose Cellulose Firmness Unfelted 3  5  Unfelted 4  8 Unfelted Unfelted Density  2.0  6.2 10.5  1.8  7.3 13.9  3.8  6.6 (pcf)Rate of 21.8 48.3 77.9 41.9 70.2 36.3 29.4 46.1 absorption (lbs/ft²/min)% Effective 28   53   53   — — — 44   — absorption

TABLE 5 Sample 8 9 C5 C9 Fine cell Fine cell Hydrophilic Hydrophilicester ester ester ester polyur- polyur- “ACQUELL” “ACQUELL” ethanerethane Firmness Unfelted 3 Unfelted  3 Rate of 5.2 8.0 21.8 48.3absorption (lbs/ft²/ min)

ACQUELL is a registered trademark of Foamex L.P.

Felting the foams according to the invention achieved surprisinglyhigher rates of water absorption and effective water absorption. Therates of water absorption for the felted foams of Examples 9 and 10 ofthe invention at various felting firmnesses exceeded the waterabsorption for other polyurethane foams and for cellulose. CompareExamples 9 and 10 with Example 8 and with Comparative Examples C5 to C9.

The invention has been illustrated by detailed description and examplesof the preferred embodiments. Various changes in form and detail will bewithin the skill of persons skilled in the art. Therefore, the inventionmust be measured by the claims and not by the description of theexamples or the preferred embodiments.

1. A method far making a hydrophilic ester polyurethane foam,comprising: (a) forming a polyurethane foam by mixing together thefollowing components: (i) 100 parts by weight of an ester polyolmixture, wherein at least 5.0 parts by weight of the ester polyolmixture comprises a hydrophilic polyester polyol made from an adipicacid and a polyethylene glycol; (ii) from 20.0 to 62.0 parts by weight,based on 100 parts polyol, of an isocyanate, wherein the isocyanateindex is 120 or less; and (iii) from 1.0 to 3.0 parts by weight, basedon 100 parts polyol, of a silicone stabilizing surfactant; (b) treatingthe polyurethane foam in a caustic bath to form the hydrophilic esterpolyurethane foam, and (c) felting the treated foam, wherein thehydrophilic ester polyurethane foam has a water absorption rate of atleast 20 pounds of water per square foot per minute.
 2. The method ofclaim 1, further comprising from 1.0 to 5.0 parts by weight, based on100 parts polyol, of a blowing agent as a component.
 3. The method ofclaim 1, wherein the blowing agent is water.
 4. The method of claim 1,further comprising as a component a catalyst selected from the groupconsisting of: gel catalysts and gas forming catalysts, and mixturesthereof.
 5. The method of claim 1, further comprising from 0.5 to 2.0parts of a blow catalyst and from 0 to 0.3 parts of a gel catalyst. 6.The method of claim 1, further comprising a double cell-forming additiveas a component.
 7. The method of claim 1, further comprising anantimicrobial additive as a component.
 8. The method of claim 1, whereinthe caustic bath is formed as a solution containing sodium hydroxide. 9.The method of claim 1, wherein the treated foam is felted by compressingthe foam to from one-third to one-eighth of its original thickness. 10.The method of claim 1, wherein the treated foam is felted by compressingthe foam while heating the treated foam to a temperature of from 340 to380° F. (171 to 193° C.).
 11. The method of claim 1, wherein beforefelting, the hydrophilic ester polyurethane foam has pore sizes in therange of 70 to 130 pores per linear inch (27.6 to 51 pores per cm). 12.The method of claim 1, wherein the isocyanate index is 100 or less. 13.The method of claim 1, wherein the hydrophilic ester polyurethane foamhas an instantaneous wet out.
 14. A hydrophilic ester polyurethane foammade according to the method of claim 1.